Free fatty acids profiling during black tea processing by 2-bromo-N,N-dimethylethanamine derivatization combined with liquid chromatography-high resolution mass spectrometry

2-Bromo- N,N -dimethylethanamine was used for fatty acids derivatization for the first time. • The derivatization method is simple, sensitive and exhibits minimal reagent residue. • The changes of 26 FFAs in different processing stages of black tea were profiled. • C16:0, C18:0, C18:2 and C18:3 displayed the most pronounced changes in black tea processing. As important precursors to aromatic substances in black tea processing, fatty acids deserve quantitative detection throughout the manufacturing procedure. We present a liquid chromatography/quadrupole orbitrap mass spectrometry method based on pre-column derivatization, which allows the simultaneous determination of 44 free fatty acids (FFAs, C3-C24). In this method, 2-bromo- N , N -dimethylethanamine was first used as a new derivatizing reagent. The derivatization system is simple and exhibits minimal reagent residue. After derivatization, the detection sensitivity of FFAs was increased by 2–4 orders of magnitude with satisfactory limit of quantitation (0.1–5 pg). Using this method, a total of 26 FFAs in black tea samples were identified and their dynamic changes at different processing stages were profiled. Among them, palmitic acid (C16:0), stearic acid (C18:0), linoleic acid (C18:2) and linolenic acid (C18:3) displayed the most pronounced changes in content and may therefore act as key indicators for monitoring black tea manufacture. Specifically, C16:0 and C18:0 exhibited a fluctuating downward trend (from 254.0 to 133.4 and 292.9 to 83.7 mg kg −1 , respectively), whereas C18:2 and C18:3 increased with fluctuations (from 18.8 to 55.0 and 13.6 to 69.2 mg kg −1 , respectively). Download: Download high-res image (142KB) Download: Download full-size image